This study focused on splicing mutations of the CFTR gene and in particular on mutations that cause a defect named exon skipping. The study was based on preliminary in vitro observation that showed the ability of small RNA molecules named Exon Specific U1 (ExSpeU1) to correct exon skipping. In this project researchers evaluated the efficacy and safety profile of this novel therapeutic approach directly in bronchial cells. They tested on primary epithelia cells (compound heterozygotes of three different splicing mutations) the efficacy of ExSpeU1s. They infected these cells with lentiviral particles expressing specific ExSpeU1s, then they assessed efficacy and safety at the level of RNA and rescue of functional CFTR activity.